Icy Spiders

Near Mars’ polar regions, spidery cracks and crevasses in the surface hold the last remnants of the winter season’s carbon dioxide frost – a.k.a. “dry ice” – which will eventually evaporate into the Martian atmosphere as CO2 gas. This process is seen on Earth only in specialized manmade situations such as when used as frozen packing material or special fog effects for a spooky setting…it’s simply too warm on Earth for carbon dioxide ice to exist naturally in any large quantity. But in Mars’ chilly climate CO2 is a major player in the natural erosion processes on the surface as it settles in layers during the winter months and then sublimates – sometimes rather forcefully! – from underlying surface layers as the climate warms in spring and summer.

The polar terrain seen here has been broken open by these processes, creating radiating cracks that resemble giant spiders or spiderwebs…hence the use of the term “araneiform” terrain when describing these areas.

Once all the dry ice has evaporated the channels will be much less visible to spacecraft like the Mars Reconnaissance Orbiter which captured this image using its HiRISE imager. They will become the same color of the surrounding landscape, waiting for the Mars winter to set in to fill them back in with a blanket of CO2 ice.